This invention relates generally to electric motors, and, more particularly, to a motor starting device.
At least some known electric motors include a start or auxiliary winding and a run winding. The start or run winding is used to initiate rotation of a motor rotor. More specifically, when the start and run windings are energized, a geometric and time phase relationship between magnetic fields generated by the run and start windings, and the magnetization of the rotor, cause the rotor to begin rotating from a standstill condition. Once the rotor has sufficient torque to attain its normal running speed, the start winding is disconnected from the motor circuit.
Start and run capacitors are sometimes used to change the time phase relationship between magnetic fields generated by the run and start or auxiliary windings. Typically, start and run capacitors are utilized in two capacitor or capacitor start capacitor-run motors. Additionally, rather than disconnecting the start winding once sufficient rotor torque is attained, the start winding can be utilized as an auxiliary run winding after motor start-up if a run capacitor is connected in series with the start winding. Using an auxiliary run winding facilitates improving motor efficiency and power factor.
A motor starting switch may be used to control energizing and de-energizing the motor start winding or start capacitor connection with an auxiliary winding. At least some known motors include a positive temperature coefficient resistor/over load resistor (PTCR/OL) to perform this switching function. For example, PTCR/OLs have been used particularly for many compressor motor applications.
One known method of securing the PTCR/OL onto a compressor is with a bail strap. The bail strap is a piece of formed spring wire that attaches to holes or slots in a compressor fence and presses against the PTCR/OL, thereby, biasing the PTCR/OL between the bail strap and a compressor shell. The bail strap prevents the PTCR/OL from disengaging from the compressor terminals due to vibration. A run capacitor is attached to the PTCR/OL, and the bail strap extends around both of them to keep the run capacitor and the PTCR/OL secured to the compressor shell.
Because of the different sizes of PTCR/OLs and capacitors, different sized straps are used for different compressor fences. Moreover, the formed spring wire bail strap may tangle and make it difficult to separate. More specifically, because the bail strap is a spring, considerable force may be required to bend it into shape for assembly onto the compressor shell and PTCR/OL.
Furthermore, as the retention force induced to the terminals increases, the removal force from the terminals is also increased, thus increasing a difficulty of assembly of the compressor. Increasing the retention force also increases an amount of stress induced to the socket material, which may cause the socket to deform. As a result, only a limited increase in retention force is possible. Moreover, lubrication that may be present on the compressor terminals may reduce the retention force available to hold the terminals to the sockets.
In one aspect, a method for retaining a terminal of a terminal assembly for a positive temperature coefficient resistor/overload resistor (PCTR/OL) assembly is provided. The method includes providing a body having an inner surface, and disposing at least one retaining member to the inner surface. The retaining member is configured to engage the terminal substantially perpendicular to an axis of symmetry of the terminal.
In another aspect, a positive temperature coefficient resistor/overload resistor (PCTR/OL) assembly includes a body having an inner surface including at least one opening therethrough. The opening is sized to receive a terminal of a terminal assembly. The PCTR/OL assembly also includes at least one retaining member attached to the inner surface. The retaining member is configured to engage the terminal substantially perpendicular to an axis of symmetry of the terminal.
In yet another aspect, a positive temperature coefficient resistor/overload resistor (PTCR/OL) assembly includes a body having an inner surface including at least one opening therethrough sized to receive a terminal of a terminal assembly. The assembly also includes at least one retaining member attached to the inner surface, and at least one conducting member having a terminal engaging end positioned within the body. The terminal engaging end includes a lance. The retaining member is electrically isolated from the conducting member.
In a further aspect, a PTCR/OL retaining system includes first retaining means for retaining a terminal substantially perpendicular to an axis of symmetry of the terminal. The system also includes second retaining means for retaining the terminal substantially parallel the terminal axis of symmetry.